In many applications, vehicular being a prime example, there is invariably a need for a regulated DC supply voltage to power small electrical motors, relays, electronic circuitry for control and instrumentation, etc. A source for this DC supply voltage is a permanent magnet alternator driven by the vehicle propulsion engine. The AC voltage generated by the alternator is then rectified and suitably filtered to derive the requisite DC supply voltage. Unfortunately, the permanent magnet alternator AC voltage is directly proportional to the speed at which it is driven by the vehicle engine. Alternator AC voltage dynamic ranges in excess of ten to one are not uncommon. Typical voltage regulators can not accommodate AC voltage dynamic ranges in excess of five to one, and multiple voltage regulators connected in cascade have been resorted to for wider dynamic ranges. This approach represents an additional expense, takes up valuable space, and adversely affects overall DC power supply reliability.
An example of an alternator having an exceptionally wide AC voltage dynamic range is a three-phase permanent magnet alternator which is widely used for control power in jet aircraft. The need for control over the full range of jet engine speeds can result in alternator AC voltages that range in excess of twenty to one. This widely varying AC voltage, once regulated to an acceptable DC voltage dynamic range, is typically applied to a switched mode type of power supply. One characteristic of a switched mode power supply is that it draws substantially constant power from the source regardless of the source voltage. Consequently, when the voltage is low, more current is drawn by the power supply to maintain a constant power input. However, due to the large series inductance of permanent magnet alternators, the AC voltage is further depressed by the higher current. Thus, when multiple regulators are used to handle AC voltage dynamic ranges exceeding the rating of a single regulator, the regulator circuit elements must be sized to accommodate these high currents. The additional power dissipation generates heat which reduces reliability and service life. On the other hand, the circuit elements must be capable of withstanding the extreme stresses imposed under high voltage conditions which are particularly acute while the DC power supply is lightly loaded.
In Applicant's commonly assigned U.S. Pat. No. 4,667,282, there is disclosed and claimed a rectifier circuit which addresses the foregoing problems. This rectifier circuit accepts an AC voltage varying over a wide dynamic range and produces a DC output voltage in which the dynamic range is compressed. This compression is achieved by monitoring the DC output voltage and automatically switching from full-wave rectification to half-wave rectification of the alternator AC voltage when a rising DC voltage reaches an upper threshold level and automatically switching from half-wave rectification to full-wave rectification when a falling DC voltage reaches a lower threshold level. The DC output voltage is thus limited to a compressed dynamic range defined by the upper and lower threshold levels as either a full-wave or a half-wave rectification of the AC source voltage.
It is accordingly an object of the present invention to provide an improved AC to DC rectifier circuit.
A further object is to provide a rectifier circuit for an AC source whose voltage varies over a wide dynamic range in which the dynamic range of the DC output voltage is compressed to a narrower dynamic range.
An additional object is to provide an AC to DC rectifier circuit providing compression of the dynamic range of the output voltage, which avoids the need for multiple stages in a subsequent voltage regulator.
Another object is to provide an AC to DC rectifier circuit providing compression of the dynamic range of the output voltage which avoids the stresses of extreme voltage and current conditions.
Yet another object is to provide an AC to DC rectifier circuit providing compression of the dynamic range of the output voltage, which is inexpensive to manufacture, efficient in operation, and reliable over a long service life.
Other objects of the invention will in part be obvious and in part appear hereinafter.